1. Field of the Invention
The subject invention relates generally to analog to digital signal conversion and more particularly to a method and apparatus operable on the output of a comparator to provide increased accuracy in the face of noise.
2. Description of Related Art
As illustrated in FIG. 1, conversion of an analog signal to a digital pulse train normally employs a comparator 11 and various analog signal processing such as analog pre-filtering 13 combined with hysterisis 15. Noise may be introduced at the input to the comparator 11, as symbolically represented at adder 17, or after analog pre-filtering, as symbolically represented at adder 19. Errors in the output pulse train result when such noise-induced error exceeds any hysterisis processing and filtering contained in the comparator 11. In cases where an extremely high pulse rate is required, such noise compromises the bandwidth and phase of the analog to digital conversion performed by the comparator 11.
According to the invention, a pulse filter is provided which prevents a pulse having a width less than a specified time duration from propagating into the pulse train at the output of the comparator. The invention operates on the output of any comparator circuit and provides a minimum pulse width rejection of any pulse which may result from noise that sets or resets the comparator. This pulse width rejection can be programmable or designed directly into the hardware/software/firmware such that a pulse less than a specified time duration will not be allowed to propagate into the pulse train.